Peter J. Dobson

The role of nanomaterials in redox-based supercapacitors for next generation energy storage devices

The development of more efficient electrical storage is a pressing requirement to meet future societal and environmental needs. This demand for more sustainable, efficient energy storage has provoked a renewed scientific and commercial interest in advanced capacitor designs in which the suite of experimental techniques and ideas that comprise nanotechnology are playing a critical role. Capacitors can be charged and discharged quickly and are one of the primary building blocks of many types of electrical circuit, from microprocessors to large-sale power supplies, but usually have relatively low energy storage capability when compared with batteries. The application of nanostructured materials with bespoke morphologies and properties to electrochemical supercapacitors is being intensively studied in order to provide enhanced energy density without comprising their inherent high power density and excellent cyclability. In particular, electrode materials that exploit physical adsorption or redox reactions of electrolyte ions are foreseen to bridge the performance disparity between batteries with high energy density and capacitors with high power density. In this review, we present some of the novel nanomaterial systems applied for electrochemical supercapacitors and show how material morphology, chemistry and physical properties are being tailored to provide enhanced electrochemical supercapacitor performance.

Sizing and phenotyping of cellular vesicles using Nanoparticle Tracking Analysis

Cellular microvesicles and nanovesicles (exosomes) are involved in many disease processes and have major potential as biomarkers. However, developments in this area are constrained by limitations in the technology available for their measurement. Here we report on the use of fluorescence nanoparticle tracking analysis (NTA) to rapidly size and phenotype cellular vesicles. In this system vesicles are visualized by light scattering using a light microscope. A video is taken, and the NTA software tracks the brownian motion of individual vesicles and calculates their size and total concentration. Using human placental vesicles and plasma, we have demonstrated that NTA can measure cellular vesicles as small as ∼50 nm and is far more sensitive than conventional flow cytometry (lower limit ∼300 nm). By combining NTA with fluorescence measurement we have demonstrated that vesicles can be labeled with specific antibody-conjugated quantum dots, allowing their phenotype to be determined. From the Clinical Editor The authors of this study utilized fluorescence nanoparticle tracking analysis (NTA) to rapidly size and phenotype cellular vesicles, demonstrating that NTA is far more sensitive than conventional flow cytometry.

Synthesis and characterization of ultra-small superparamagnetic iron oxide nanoparticles thinly coated with silica

Ultra-small superparamagnetic iron oxide nanoparticles (SPIOs) were synthesized by co-precipitation of iron chloride salts with ammonia and then encapsulated with thin (~2nm) layers of silica. The particles have been characterized for size, diffraction pattern, surface charge, and magnetic properties. This rapid and economical synthesis has a number of industrial applications; however, the silica-coated particles have been optimized for use in medical applications as MR contrast agents, biosensors, DNA capturing, bioseparation and enzyme immobilization.

High resolution x-ray photoemission study of plasma oxidation of indium–tin–oxide thin film surfaces

The influence of plasma oxidation and other surface pretreatments on the electronic structure of indium–tin–oxide (ITO) thin films has been studied by high resolution x-ray photoemission spectroscopy. Plasma oxidation compensates n-type doping in the near surface region and leads to a reduction in the energy of plasmon satellite structure observed in In 3d core level spectra. In parallel, the Fermi level moves down within the conduction band, leading to a shift to low binding energy for both core and valence band photoemission features; and the work function increases by a value that corresponds roughly to the core and valence band binding energy shifts. These observations suggest that the conduction band of ITO is fixed relative to the vacuum level and that changes of work function are dominated by shifts of the Fermi level within the conduction band.

The impact of zero-valent iron nanoparticles on a river water bacterial community

Zero-valent iron (ZVI) nanoparticles are of interest because of their many potential biomedical and environmental applications. However, these particles have recently been reported to be cytotoxic to bacterial cells. The overall objective of this study was to determine the impact of 100mg/L ZVI nanoparticles on the diversity and structure of an indigenous river water bacterial community. Response during exposure for 36 days was determined by denaturing gel gradient electrophoresis (DGGE) analysis of bacterial 16S rRNA genes, amplified from extracted DNA, and viable and total cell abundances were determined by plate counting and fluorescent microscopy of DAPI-stained cells. Changes in river water chemistry were also monitored. Addition of ZVI nanoparticles led to a rapid decrease in oxidation-reduction potential (ORP) (+196 to -281 mV) and dissolved oxygen (DO) concentration (8.2-0.6 mg/L), both of which stabilized during the experiment. Interestingly, both viable and total bacterial cell abundances increased and pH decreased, characteristic of an active microbial community. Total community structure was visualized using rank-abundance plots fitted with linear regression models. The slopes of the regression models were used as a descriptive statistic of changes in evenness over time. Importantly, despite bacterial growth, addition of ZVI nanoparticles did not influence bacterial community structure.

A facile route to CdTe nanoparticles and their use in bio-labelling

A simple synthetic route to highly luminescent, water-soluble CdTe nanoparticles and their use in biological imaging is presented. The new synthetic pathway utilises a simply-prepared, water-soluble tellurium precursor which is easily handled and stored and the resulting growth processes are discussed.

Growth of In2O3(100) on Y-stabilized ZrO2(100) by O-plasma assisted molecular beam epitaxy

Thin films of In2O3 have been grown on Y-stabilized ZrO2(100) by oxygen plasma assisted molecular beam epitaxy with a substrate temperature of 650°C. Ordered epitaxial growth was confirmed by high resolution transmission electron microscopy. The position of the valence band onset in the x-ray photoemission spectra of the epitaxial films is found to be inconsistent with the widely quoted value of 3.75eV for the fundamental bandgap of In2O3 and suggests a revised value of 2.67eV.

Power law carrier dynamics in semiconductor nanocrystals at nanosecond timescales

We report the observation of power law dynamics on nanosecond to microsecond timescales in the fluorescence decay from semiconductor nanocrystals and draw a comparison between this behavior and power law fluorescence blinking from single nanocrystals. The link is supported by comparison of blinking and lifetime data measured simultaneously from the same nanocrystal. Our results reveal that the power law coefficient changes little over the nine decades in time from 10nsto10s, in contrast with the predictions of some diffusion based models of power law behavior.

Dual mode electron emission from ferroelectric ceramics

Two modes of electron emission have been observed from the ferroelectric ceramic PLZT when subjected to a high voltage bipolar pulse. One mode is always associated with bright visible plasma on the emitting surface, while the other occurs with no visible emission. Emitted current wave forms are consistent with two distinct mechanisms for emission: surface plasma in the first case and polarization switching in the second.

A novel hybrid nano zerovalent iron initiated oxidation--biological degradation approach for remediation of recalcitrant waste metalworking fluids.

Disposal of operationally exhausted metal working fluids (MWF) through a biological route is an attractive option, since it is effective with relatively low energy demands. However, it is enormously challenging since these fluids are chemically complex, including the addition of toxic biocides which are added specifically to retard bio-deterioration whilst the fluids are operational. Nano-sized elemental iron represents a new generation of environmental remediation technologies. Laboratory scale batch studies were performed to test the degradation ability of a semi-synthetic metalworking fluid (MWF) wastewater (which was found to be resistant to initial bacterial treatment in specifically established bioreactors) by employing a novel hybrid approach. The approach was to combine the synergistic effects of nano zerovalent iron (nZVI) induced oxidation, followed by biodegradation, specifically for the remediation of recalcitrant components of MWF effluent. Addition of nZVI particles to oxygenated wastewater resulted in oxidation of organic contaminants present. Our studies confirmed 78% reduction in chemical oxygen demand (COD) by nZVI oxidation at pH 3.0 and 67% reduction in neutral pH (7.5), and 85% concurrent reduction in toxicity. Importantly, this low toxicity made the nZVI treated effluent more amenable for a second stage biological oxidation step. An overall COD reduction of 95.5% was achieved by the novel combined treatment described, demonstrating that nZVI oxidation can be exploited for enhancing the biodegradability of a recalcitrant wastewater in treatment processes.